Jonathan B. Losos

IMPROBABLE DESTINIES

How Predictable is Evolution?

Book review by Anthony Campbell. The review is licensed under a Creative
Commons Licence.
An important controversy in evolutionary biology concerns the
inevitability or otherwise of the appearance of humans. According to
Steven J. Gould, if the tape of life could be rerun from the beginning
it is very unlikely that anything resembling humans would appear. But
Simon Conway Morris disagrees. He and those who think like him hold
that something very similar to us was pretty well bound to arise, and
similar organisms would evolve on any other planets that support complex
life (though these are likely to be rare). So who is right? This is the
question that Losos tackles in his new book.

The main evidence that Conway Morris cites to support his thesis comes
from convergent evolution. This refers to the independent evolution of
similar features in different lineages; for example, birds, bats,
pterosaurs, and insects all evolved the ability to fly although in
different ways. Conway Morris's book, Life's
Solution: Inevitable Humans in a Lonely Universe, provides a huge
number of examples of convergence.

This is certainly impressive. But the cases he cites are all
retrospective; they describe convergences that have developed over very
long periods. This is how we normally think of evolution, as
a slow process taking thousands or millions of years. But what Losos
writes about is modern experiments showing that in some circumstances
evolution can occur extremely rapidly—in fact, over just a few
generations.

Losos is himself involved in this kind of research and describes his
own experience, but there is also a lot of information about the work of
others. The book is written in a very accessible style and will hold the
interest of anyone who has wondered about the question it addresses. In
part this is because Losos uses almost a detective-story method; he
doesn't tell us his own view at the outset but works up to it in his
final section (so I won't give it away here).

The book is in three parts. Part 1 is a survey of examples of
convergence. Losos agrees with Conway Morris that these often
astonishing cases present a challenge to Gould's view. But there is also
counter-evidence in the form of animals and plants that have evolved
only once and are therefore unique. A prime example is the Platypus,
with its duck-like bill, poisonous spurs, and egg-laying reproduction.
Nothing like it ever appeared outside Australia, yet there are
habitats in other continents where it might have flourished if it had
evolved there. Then there is Madagascar, which produced, among many
other curiosities now extinct, vegetarian crocodiles and the elephant
bird that was ten feet tall and half a ton in weight.

At the end of his historical survey Losos finds the case for
inevitability to be suggestive but not conclusive.

Conway Morris and his colleagues are to be commended for
bringing convergent evolution to the forefront. We all knew about
convergence as a neat trick of natural history, a striking example of
the power of natural selection. But Conway Morris and company have made
clear that evolutionary duplication is much more common than we
realized. We now recognize that it's a frequent occurrence in the
natural world, with examples all around us. Still, it's far from
ubiquitous. Seemingly just as often, maybe more often, species living in
similar environments don't adapt convergently.

Part 2 is where Losos reports on experiments in evolution done by
himself and many others. A commonly used method is to isolate
populations of various species such as fish or lizards (Losos's
favourite subjects) in a new habitat, perhaps accompanied by a
predator, and see how they evolve.

The fish studied by Losos were in remote jungle areas of Trinidad;
research lasted over years or even decades and was sometimes quite
dangerous owing to snakes and other hazards. All this is described
entertainingly but the experiments evidently required a huge amount of
dedication.

Losos's lizard experiments were done on small rocky islands in the
Caribbean. They were usually less risky for the experimenters but they
had their own hazards, notably hurricanes, which ended several promising
experiments prematurely. Other researchers have worked in more
artificial environments, either in the laboratory or outdoors, in
specially engineered settings.

Evolution often happened with astonishing rapidity in these setups, over
just a few generations. But this is obviously very different from the
huge natural time scale of biological evolution over millions of years
and generations. Yet it is possible to approach such time scales by
using bacteria, which produce new generations much more
quickly—every 20 minutes for some species. Work done in this way
by Rich Lenski has yielded fascinating results, including a totally
unexpected mutation allowing the bacteria to use citrate, something
never seen in this species before.

[The new mutation] left only one conclusion: this single
population that had lived in flasks for fourteen years in the Lenski
Lab had made a major evolutionary leap. Somehow, through the right
combination of mutations and natural selection, the population had
evolved an adaptation that, as far as anyone knows, this species had
never been able to produce in millions of years of its evolution in the
wild.

At one time Lenski's work seemed to be a strong confirmation of the
predictability of evolution, but now Lenski himself thinks that this
needs to be modified.

The book is written with a lot of humour and contains plenty of
background anecdotal information, yet you are reading real science,
not gossip. At the end of Part 3 I felt I had been given a convincing
answer to the Gould–Conway controversy. The excellent drawings
by Marlin Peterson add to the pleasure of reading, even in the Kindle
version.